Having issues with larger tire programming for accurate speedo

[mtrosclair]

2022 Timberline, I'm having an issue with getting the new tire size to work and I am looking for advice or guidance.

I posted it in the gen 4 forum when I understood even less but with no replies.

2022 Timberline Tire size adjustment with forscan

So, I finally got new tires and I need some help because for some reason I am not understanding how to figure out getting the tire size in forscan correct. Long story short I decided on the Firestone Destination XT and they were not available in the stock size of 265 70 r18 with the white...

www.expeditionforum.com

Stock is 265/70 r18, new tires are LT275/70r18, I initially just tried changing the circumference in the plain english part of FORscan but the speedo was 3.5 mph over actual. After learning that a PCM relearn was needed I also learned that the maximum diameter value it will accept is 2610mm, which still gives a 2 mph discrepancy. The value would need to be 2649mm from what I can find to produce an accurate result. Looking at some F-150 forums there do appear to be ways around this but I realize there may be differences with the Expedition.

 

[HILLY]

You discovered this as well...

I tried to do an update to my tire size prior to a road trip to compensate for my tire size (315/70R17) as I'm running about 4 MPH over at highway speeds. I think I was trying to input a value of ~2655mm (Bronco Sasquatch value) but the truck didn't like it, so I went back to stock. Looking further into this I later found out that supposedly the max size is 2546 (09F2) which I haven't done yet. If you are saying 2610 works, that's better yet and helps minimize the discrepancy.

Only other solution I've heard of is to contact a tuner and they can add it to the programming device to correct the tire size. It's either an expensive way to go to get a correct speedo or a cheap by-product of getting a tune, however you look at it.

 

[mtrosclair]

You discovered this as well...

I tried to do an update to my tire size prior to a road trip to compensate for my tire size (315/70R17) as I'm running about 4 MPH over at highway speeds. I think I was trying to input a value of ~2655mm (Bronco Sasquatch value) but the truck didn't like it, so I went back to stock. Looking further into this I later found out that supposedly the max size is 2546 (09F2) which I haven't done yet. If you are saying 2610 works, that's better yet and helps minimize the discrepancy.

Only other solution I've heard of is to contact a tuner and they can add it to the programming device to correct the tire size. It's either an expensive way to go to get a correct speedo or a cheap by-product of getting a tune, however you look at it.

Yes, I got to 2610 by trial and error, that is disappointing that I need a tuner for such a small tire size change.

 

[Mr Big]

Yes, I got to 2610 by trial and error, that is disappointing that I need a tuner for such a small tire size change.

They don't allow it the easy way, because they do not want the tire height changed for obvious reasons. I've changed many wheel and tire sizes on vehicles, but never changed the height.

 

[HILLY]

Yes, I got to 2610 by trial and error, that is disappointing that I need a tuner for such a small tire size change.

I had a little bit of time last night to go back at this again eager to try your 2610 finding. Could not get this number to work and so I went with 2546 which did. Quick test drive comparing cluster vs. phone GPS had me at ~1.5 mph faster in the 70-80 mph range as opposed to it previously being 4-5 mph faster. At town speeds it was pretty much right on, i.e. - 45 = 45.

For now I'll take that.

 

[Mr Big]

I had a little bit of time last night to go back at this again eager to try your 2610 finding. Could not get this number to work and so I went with 2546 which did. Quick test drive comparing cluster vs. phone GPS had me at ~1.5 mph faster in the 70-80 mph range as opposed to it previously being 4-5 mph faster. At town speeds it was pretty much right on, i.e. - 45 = 45.

For now I'll take that.

It's too bad you weren't able to shop for the stock size and had to use a different tire size? It's always best to stick with the factory suggested tire height. Even though this was not your case. Whenever I want bigger or smaller diameter rims, I use a tire size calculator to determine what tire size I need to maintain the same diameter. Tire Size Calculator
Did you have the latest version of Forscan?

 

[HILLY]

It's too bad you weren't able to shop for the stock size and had to use a different tire size? It's always best to stick with the factory suggested tire height. Even though this was not your case. Whenever I want bigger or smaller diameter rims, I use a tire size calculator to determine what tire size I need to maintain the same diameter. Tire Size Calculator
Did you have the latest version of Forscan?

Not sure what shopping for the stock size has to do with my situation since I lifted and went with 35's as my end goal; more specifically the Sasquatch/Raptor size. My personal thing is if I upgrade tire sizes I try to stick with commonly available tread for emergencies as opposed to unique sizes. I'm only trying to compensate and mitigate the upsize I did as a result. Besides achieving more accurate speed, I'm trying to track mileage as close as possible, otherwise I would've just carried on and lived with it. I had assumed that I would be able to program in the spec Ford uses for Raptors/Sasquatch's since I was staying within a range used in factory production.

Aside from that, I am a paid subscriber to FORScan and I think I've had my version 2.3.66 when it released in May since that is when I did my lift. I checked again last night to see if there were any updated versions prior to working on the programming, but it looks like I had the latest. Programming the tire size seems to be limited by the available range within the BCM as noted by others. There also must be further variations by MY and possibly trims since mtrosclair (MY22 Timberline) is able to go "bigger" than I with 2610 mm. I could have tried experimenting more, but it was late and I was running out of time.

 

[Mr Big]

Not sure what shopping for the stock size has to do with my situation since I lifted and went with 35's as my end goal; more specifically the Sasquatch/Raptor size.

I misunderstood. I understand now you went to 35s.

 

[Shotgun76]

Thought I saw that FORScan just released an update last week?

 

[HILLY]

Thought I saw that FORScan just released an update last week?

Looks like there is a small update as it went from 2.3.66 --> 2.3.67. This type of update (major.minor.patch) is usually just a patch to fix bugs. A 'minor' update would add features.

I still doubt that FORScan will be able to do much with this as I still believe that limitations are within the BCM as I've read various platforms hitting MIX/MAX limits (Broncos, F150's, etc.). There would have to be be a means to do a major reflash of the module to open up these limits.

 

[Mr Big]

I watched this and it worked for me to adjust tire size over 2649, using the latest paid version of FORScan
Tire size adjustment - Forscan

 

[mseymour67]

Good info. Been thinking about going up a size on my Expy.